It turns out, though, that Okinawan long life expectancy was actually due to rampant pension fraud rather than long life. I can't remember the exact date, but it would have been around 2008, a reporter went to visit the oldest people in Japan (most of whom were living in Okinawa). They started at the oldest and found that the person wasn't home ("visiting relatives"). So they went to the next oldest. Similar story. They went through the top 20 and couldn't find any of them.

The government clued in and investigated and it turns out that Okinawan doctors were making a tidy profit by agreeing not to file death certificates. This enabled families to continue to claim pension benefits on behalf of their supposedly aged relatives.

After the the smoke died down the went back and looked at Okinawan life expectancy taking pension fraud into consideration and discovered that it was pretty much exactly the same as the rest of Japan. The original life expectancy/diet studies had relied on government information rather than actually interviewing people. I'm sorry I don't have a citation for you as I saw this in a documentary in Japan on TV.